Magnetism and Thermoelectric Properties of the Zintl Semiconductor: EuZnAs.

Compositional diversity and intriguing structural features have made Zintl phases excellent candidates as thermoelectric materials. Zintl phase with 21-4-18 composition has shown high thermoelectric performance in the mid- to high-temperature ranges. The complex crystal structure and favorable transport properties of these compounds indicate the potential for high thermoelectric efficiency.

Probabilistic prediction of material stability: integrating convex hulls into active learning.

Active learning is a valuable tool for efficiently exploring complex spaces, finding a variety of uses in materials science. However, the determination of convex hulls for phase diagrams does not neatly fit into traditional active learning approaches due to their global nature. Specifically, the thermodynamic stability of a material is not simply a function of its own energy, but rather requires energetic information from all other competing compositions and phases.

Into the Void: Single Nanopore in Colloidally Synthesized BiTe Nanoplates with Ultralow Lattice Thermal Conductivity.

BiTe is a well-known thermoelectric material that was first investigated in the 1960s, optimized over decades, and is now one of the highest performing room-temperature thermoelectric materials to-date. Herein, we report on the colloidal synthesis, growth mechanism, and thermoelectric properties of BiTe nanoplates with a single nanopore in the center. Analysis of the reaction products during the colloidal synthesis reveals that the reaction progresses via a two-step nucleation and epitaxial growth: first of elemental Te nanorods and then the binary BiTe nanoplate growth.

High Thermoelectric Performance in 2D SbTe and BiTe Nanoplate Composites Enabled by Energy Carrier Filtering and Low Thermal Conductivity.

Thermoelectrics are an important class of materials with great potential in alternative energy applications. In this study, two-dimensional (2D) nanoplates of the layered chalcogenides, SbTe and BiTe, are synthesized and composites of the two are investigated for their thermoelectric properties. The two materials, SbTe and BiTe, were synthesized as hexagonal, 2D nanoplates via a colloidal polyol route.

β-Phase YbSbH: Magnetic and Thermoelectric Properties Traversing from an Electride to a Semiconductor.

An electride is a compound that contains a localized electron in an empty crystallographic site. This class of materials has a wide range of applications, including superconductivity, batteries, photonics, and catalysis. Both polymorphs of YbSb (the orthorhombic CaSbF structure type (β phase) and hexagonal MnSi structure type (α phase)) are known to be electrides with electrons localized in 0D tetrahedral cavities and 1D octahedral chains, respectively.

Alloying-Induced Structural Transition in the Promising Thermoelectric Compound CaAgSb.

AMX Zintl compounds, crystallizing in several closely related layered structures, have recently garnered attention due to their exciting thermoelectric properties. In this study, we show that orthorhombic CaAgSb can be alloyed with hexagonal CaAgBi to achieve a solid solution with a structural transformation at ∼ 0.8.

Anisotropic proximity-induced superconductivity and edge supercurrent in Kagome metal, KVSb.

Materials with Kagome nets are of particular importance for their potential combination of strong correlation, exotic magnetism, and electronic topology. KVSb was discovered to be a layered topological metal with a Kagome net of vanadium. Here, we fabricated Josephson Junctions of KVSb and induced superconductivity over long junction lengths.

Investigating the Role of Vacancies on the Thermoelectric Properties of EuCuSb-Eu ZnSb Alloys.

AMX compounds with the ZrBeSi structure tolerate a vacancy concentration of up to 50 % on the M-site in the planar MX-layers. Here, we investigate the impact of vacancies on the thermal and electronic properties across the full EuCu Zn Sb solid solution. The transition from a fully-occupied honeycomb layer (EuCuSb) to one with a quarter of the atoms missing (EuZn Sb) leads to non-linear bond expansion in the honeycomb layer, increasing atomic displacement parameters on the M and Sb-sites, and significant lattice softening.

Thermoelectric Properties of BaEuZnSb, a Zintl Phase with One-Dimensional Covalent Chains.

The compound BaZnSb has been predicted to be a promising thermoelectric material, potentially achieving > 2 at 900 K due to its one-dimensional chains of edge-shared [ZnSb] tetrahedra and interspersed Ba cations. However, the high air sensitivity of this material makes it difficult to measure its thermoelectric properties. In this work, isovalent substitution of Eu for Ba was carried out to make BaEuZnSb in order to improve the stability of the material in air and to allow characterization of thermal and electronic properties of three different compositions ( = 0.

Study of the Thermoelectric Properties of BiTe/SbTe Core-Shell Heterojunction Nanostructures.

Thermoelectric materials convert heat energy into electricity, hold promising capabilities for energy waste harvesting, and may be the future of sustainable energy utilization. In this work, we successfully synthesized core-shell BiTe/SbTe (BTST) nanostructured heterojunctions via a two-step solution route. Samples with different BiTe core to SbTe shell ratios could be synthesized by controlling the reaction precursors.

Giant, unconventional anomalous Hall effect in the metallic frustrated magnet candidate, KVSb.

The anomalous Hall effect (AHE) is one of the most fundamental phenomena in physics. In the highly conductive regime, ferromagnetic metals have been the focus of past research. Here, we report a giant extrinsic AHE in KVSb, an exfoliable, highly conductive semimetal with Dirac quasiparticles and a vanadium Kagome net.

Alloyed Thermoelectric PbTe-SnTe Films Formed via Aerosol Deposition.

The discovery of new thermoelectric materials has the potential to benefit from advances in high-throughput methodologies. Traditional synthesis and characterization routes for thermoelectrics are time-consuming serial processes. In contrast, high-throughput materials discovery is commonly done by thin film growth, which may produce microstructures that are metastable or compositionally graded and, therefore, are challenging to characterize.

Thermoelectricity in transition metal compounds: the role of spin disorder.

At room temperature and above, most magnetic materials adopt a spin-disordered (paramagnetic) state whose electronic properties can differ significantly from their low-temperature, spin-ordered counterparts. Yet computational searches for new functional materials usually assume some type of magnetic order. In the present work, we demonstrate a methodology to incorporate spin disorder in computational searches and predict the electronic properties of the paramagnetic phase.

Understanding and Control of Bipolar Self-Doping in Copper Nitride.

Semiconductor materials that can be doped both n-type and p-type are desirable for diode-based applications and transistor technology. Copper nitride (CuN) is a metastable semiconductor with a solar-relevant bandgap that has been reported to exhibit bipolar doping behavior. However, deeper understanding and better control of the mechanism behind this behavior in CuN is currently lacking in the literature.

Effect of extended strain fields on point defect phonon scattering in thermoelectric materials.

The design of thermoelectric materials often involves the integration of point defects (alloying) as a route to reduce the lattice thermal conductivity. Classically, the point defect scattering strength follows from simple considerations such as mass contrast and the presence of induced strain fields (e.g.

Measurement of the electrical resistivity and Hall coefficient at high temperatures.

The implementation of the van der Pauw (VDP) technique for combined high temperature measurement of the electrical resistivity and Hall coefficient is described. The VDP method is convenient for use since it accepts sample geometries compatible with other measurements. The technique is simple to use and can be used with samples showing a broad range of shapes and physical properties, from near insulators to metals.

A high temperature apparatus for measurement of the Seebeck coefficient.

A high temperature Seebeck coefficient measurement apparatus with various features to minimize typical sources of error is designed and built. Common sources of temperature and voltage measurement error are described and principles to overcome these are proposed. With these guiding principles, a high temperature Seebeck measurement apparatus with a uniaxial 4-point contact geometry is designed to operate from room temperature to over 1200 K.

Predicted electronic and thermodynamic properties of a newly discovered Zn8Sb7 phase.

A new binary compound, Zn(8)Sb(7), has recently been prepared in nanoparticulate form via solution synthesis. No such phase is known in the bulk phase diagram; instead, one would expect phase separation to the good thermoelectric semiconductors ZnSb and Zn(4)Sb(3). Here, density functional calculations are employed to determine the free energies of formation, including effects from vibrations and configurational disorder, of the relevant phases, yielding insight into the phase stability of Zn(8)Sb(7).

Synthesis, structure, magnetism, and high temperature thermoelectric properties of Ge doped Yb14MnSb11.

The Zintl phase Yb(14)MnSb(11) was successfully doped with Ge utilizing a tin flux technique. The stoichiometry was determined by microprobe analysis to be Yb(13.99(14))Mn(1.

Electronic structure and transport in thermoelectric compounds AZn2Sb2 (A = Sr, Ca, Yb, Eu).

The AZn(2)Sb(2) (P3m1, A = Ca, Sr, Eu, Yb) class of Zintl compounds has shown high thermoelectric efficiency (zT approximately 1) and is an appealing system for the development of Zintl structure-property relationships. High temperature transport measurements have previously been conducted for all known compositions except for SrZn(2)Sb(2); here we characterize polycrystalline SrZn(2)Sb(2) to 723 K and review the transport behavior of the other compounds in this class. Consistent with the known AZn(2)Sb(2) compounds, SrZn(2)Sb(2) is found to be a hole-doped semiconductor with a thermal band gap approximately 0.

Enhancement of thermoelectric efficiency in PbTe by distortion of the electronic density of states.

The efficiency of thermoelectric energy converters is limited by the material thermoelectric figure of merit (zT). The recent advances in zT based on nanostructures limiting the phonon heat conduction is nearing a fundamental limit: The thermal conductivity cannot be reduced below the amorphous limit. We explored enhancing the Seebeck coefficient through a distortion of the electronic density of states and report a successful implementation through the use of the thallium impurity levels in lead telluride (PbTe).

Complex thermoelectric materials.

Thermoelectric materials, which can generate electricity from waste heat or be used as solid-state Peltier coolers, could play an important role in a global sustainable energy solution. Such a development is contingent on identifying materials with higher thermoelectric efficiency than available at present, which is a challenge owing to the conflicting combination of material traits that are required. Nevertheless, because of modern synthesis and characterization techniques, particularly for nanoscale materials, a new era of complex thermoelectric materials is approaching.

Template-free routes to porous inorganic materials.

New approaches to solid-state reactivity have allowed us to develop unusual routes to porous inorganic materials. This article describes our recent work on template-free routes involving the selective leaching of one phase from a two-phase composite to form porous oxides. Subsequent reactions have been developed to yield porous metals, conformal coatings, and hierarchically porous materials.